Abstract

Measurements of low-frequency noise in thick-film resistors at low temperatures are reported. Films were prepared in a standard “high temperature” process: 20 nm sized powder was mixed with granular lead–borosilicate glass and organic solvent to give a paste, which was then screen printed onto alumina substrates and fired in a tunnel furnace. Measurements below liquid helium temperature reveal that the low frequency noise increases with decreasing temperature, approximately as , . Up to 4 T no dependence of noise intensity on magnetic field has been observed. Measurements of noise spectra in the range show that spectral and temperature slopes obey Dutta, Dimon, and Horn equation [Phys. Rev. Lett.43, 646 (1979)] only in the range . Below this temperature a gap of constant width opens between noise exponent calculated from the spectral slope and from temperature dependence of noise magnitude. This gap occurs due to the change of noise coupling mechanism that takes place at . At higher temperatures this coupling is temperature independent. At lower temperatures coupling becomes temperature dependent. It is shown that data agree quantitatively with the concept that noise sources modulate energies for thermally activated hops in the percolation network.